The present invention relates to a safety device for a number of electrical loads, and a method for shutting off a number of electrical loads.
In control units for antilock braking systems, slip control regulating systems, and vehicle dynamics control systems, solenoid valves are used to adjust the respective manipulated variables. For safety reasons, it must be possible to shut off the solenoid valves via two shutoff paths. In a first shutoff path, which makes possible individual activation or shutoff of individual solenoid valves of a quantity of solenoid valves during normal operation, low-side drivers serve as the activation elements. What is used as the second shutoff path for the solenoid valves is usually a semiconductor switch element or a magnetic relay, to be arranged in the high-side path (supply line). This ensures that even in the event of an irreversible defect in a low-side driver (activation system), the solenoid valves (loads) can be shut off in order to avoid a safety-critical condition.
It is regarded as disadvantageous in circuits of this kind that expensive semiconductor switches requiring a complex protective structure, or bulky mechanical relays, must be used in order to guarantee safety.
German Published Patent Application No. 29 35 196 discusses a safety device for electrical loads in motor vehicles, having a current flow sensing member and a control device for a current flow interrupter, in which the current flow through the load is sensed by way of an RC element, and the control device comprises a threshold value switch, to which the output signal of the RC element is delivered and whose output signal controls a current interrupter switch.
An object of the present invention is the provision of a circuit with which a second shutoff path for a number of electrical loads (in particular solenoids) that is necessary for safety reasons can be implemented in simple and economical fashion.
According to the present invention, it is now possible to eliminate the expensive semiconductor switches together with their protective structure, or bulky mechanical relays, that were conventionally used. Because the defect in a driver is irreversible, it is sufficient to bring about permanent interruption of the supply line. Any additional switching function in the supply line by way of an electronic or electromagnetic relay can be dispensed with without incurring disadvantages.
It is possible, in particular by specific activation of, for example, all the loads by way of the corresponding drivers (which represents an abnormal operating state), to generate in the supply line a current strength or intensity that causes the fuse to respond. It is also conceivable to activate only some of the other drivers in a situation of this kind. All that is important is to make available sufficient current strength for the fuse to respond. Activation of each of the drivers can be brought about by way of a suitable control device that is configured, for example, with a monitoring logic system that detects a defect in a driver (a monitoring logic system of this kind is capable of detecting a defect, but is not in a position to remedy a defect). It is also possible to configure each drivers with a monitoring logic system of this kind.
According to a preferred embodiment of the safety device according to the present invention, provision is made for the loads to be located between a high-side path and a low-side path of the supply line, the drivers being provided on the low-side path and the fuse on the high-side path. This makes available a particularly simple and reliable safety device which exploits the fact that, in contrast to conventional safety apparatuses, a relatively high current can be generated in the high-side path by activating a predetermined number of loads. By way of a current of this kind, the correspondingly dimensioned fuse can be caused to respond in suitable fashion. A defect in the activation system of a load can be detected, for example, by way of a monitoring logic system of the drivers or activation ICs provided in the low-side path.
Advantageously, the fuse used in the safety device is a blow-out fuse. Blow-out fuses of this kind are available at low cost in a plurality of sizes and power ranges. The fuse can also be implemented, for example, by selection of a suitable conductor path geometry.
Advantageously, the loads are, in particular, solenoid valves usable in antilock braking, slip control, or vehicle dynamics control systems. Solenoid valves of this kind can be easily and reliably operated using safety devices according to the present invention.